Answer :
The number of moles of hydrogen gas produced is approximately 0.278 mol. The work done by the system is approximately -7420.98 kJ. The change in internal energy of the system is approximately -7519.78 kJ.
To calculate the number of moles of hydrogen gas produced and the work done by the system, we need to use the First Law of Thermodynamics, which states that the change in internal energy of a system is equal to the heat absorbed or released by the system plus the work done on or by the system.
Given:
Mass of aluminum (Al) = 5.00 g
Heat expelled by the system = -99.8 kJ
Pressure (P) = 1 atm
Temperature (T) = 298 K
Gas constant (R) = 8.314 x 10³ kJ mol⁻¹ K⁻¹
First, let's calculate the moles of aluminum used:
Molar mass of Al = 26.98 g/mol
moles of Al = mass of Al / molar mass of Al = 5.00 g / 26.98 g/mol ≈ 0.185 mol
From the balanced chemical equation, we know that 2 moles of Al react to produce 3 moles of H2. Therefore, the moles of H2 produced will be:
moles of H2 = (3/2) * moles of Al = (3/2) * 0.185 mol ≈ 0.278 mol
Next, let's calculate the work done by the system using the ideal gas law:
Work = -PΔV
Since the reaction produces gas (H2), the work done can be calculated by:
Work = -P * Δn * R * T
where Δn is the change in the number of moles of gas (moles of products - moles of reactants).
Δn = (3 - 0) = 3 moles
Work = -P * Δn * R * T = -(1 atm) * (3 mol) * (8.314 x 10³ kJ mol⁻¹ K⁻¹) * (298 K)
Work ≈ -7420.98 kJ
The negative sign indicates work done by the system.
Finally, using the First Law of Thermodynamics, we can calculate the change in internal energy of the system:
ΔU = q + w
ΔU = (-99.8 kJ) + (-7420.98 kJ) = -7519.78 kJ
The negative sign indicates that the internal energy of the system has decreased.
Therefore, the number of moles of hydrogen gas produced is approximately 0.278 mol, the work done by the system is approximately -7420.98 kJ, and the change in internal energy of the system is approximately -7519.78 kJ.
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